Transport mechanisms of the retinal pigment epithelium to maintain of visual function

In the visual process the interaction between the retinal pigment epithelium (RPE) and photoreceptors involves several transport phenomena. Heat from light-absorption is eliminated by blood-flow in the choroid. Transepithelial transport eliminates water from subretinal space for close interaction between photoreceptors and RPE. A recycling transport supplies the chromophore for photoreceptors. Last but not least transmembranal K+ transport maintains excitability of photoreceptors and Ca2+ enables the regulation of RPE function.